In forming a bonded Gas Diffusion Layer (GDL) and gasket of a fuel cell, the GDL is inserted by a tool and formed by injection molding. In doing this, the gasket is formed higher than the GDL in some cases, but if sealing on the back surface is required the gasket must be formed at the end of the GDL. In doing this, the strength of the bond between rubber and GDL is critical to assure the durability of the gasket. One method used in order to obtain low-cost goods while maintaining sufficient bonding strength in formation is to impregnate a portion of the GDL with rubber, however in configurations such as shown in FIG. 3 whereby gasket 52 is located outside GDL 51, result in difficulties in that the general thinness of the GDL prevents sufficient bonding strength. In FIG. 3, symbol 51 indicates the GDL, 52 indicates a gasket around its edge and formed as one unit therewith, and 53 indicates the rubber-impregnated part that causes gasket 52 to be formed as one unit with GDL 51.
As a means of resolving the above difficulty, methods exist of obtaining bond strength by causing gasket 52 and GDL 51 to overlap so as to increase the contact surface area, as shown in FIG. 4 and FIG. 5. The GDL, however, is an elastic material with high porosity and therefore low strength, so that when the flow of rubber in the GDL does not stop at the specified position, problems of defective formation occur as shown in FIG. 6, such as when a curvature S (see FIG. 6A) or fold O (see FIG. 6B) is formed on GDL 51. The reason that rubber does not stop at the specified position on GDL 51 is that GDL 51 is compressed and greatly deformed by the fastening part (T in FIG. 5) of tool 61, and therefore GDL 51 is bent upward by tensile stress created in the boundary end surface thereof, and the rubber ejection pressure is applied while it is in that state. Further, it is recognized that curvature of FDL 51 after forming can be restricted by reducing the compression ratio of GDL 51, however in this case the rubber material flows into the inside of GDL 51, giving rise to the problem that the reactive surface is reduced by the electro-generative operation of GDL 51. Because of the high porosity of GDL 51, in order to restrict the flow of rubber material it is necessary to close the tool with high compression of approximately 30-50%, and therefore it is difficult to restrict curvature in GDL 51.
Reference documents regarding prior art    Patent document 1 Patent Announcement JP2009-064769    Patent document 2 Patent Announcement JP2007-026847